Fisher 1280x help

[rocketmoon2]

I just aquired an older Fisher 1280x, I have already ordered a battery cover gasket as the old one was in pretty bad shape. The detector turns on, and functions on dry land great, but the previous owner stated it hasent been in the water in a while. My questions are what type of grease should the "o"-ring seals for the control knobs get? and is there anything else i should be watchfull of? thanks for any replies, this is my first water detector so this is new to me.